18. I am not sure whether I can gain any profit from the investment, so I can’t make a(n) ____ promise to help you. A. exact B. defined C. definite D. sureinvestment 投资investigate 调查irrigate 灌溉irritable 激怒的navigate 航行castigate 惩罚mitigate 缓和，调解，减轻 sure 确信insure 保险ensure 确保define 限定，下定义final 结束的refine 提纯finance 财政，资金